Expression vectors and cell lines expressing vascular endothelial growth factor D

ABSTRACT

This invention relates to expression vectors comprising VEGF-D and its biologically active derivatives, cell lines stably expressing VEGF-D and its biologically active derivatives, and to a method of making a polypeptide using these expression vectors and host cells. The invention also relates to a method for treating and alleviating melanomas or tumors expressing VEGF-D and various diseases.

This application claims the benefit of prior filed, provisionalapplication No. 60/087,392, filed May 29, 1998.

BACKGROUND OF THE INVENTION

This invention relates to expression vectors comprising VEGF-D and itsbiologically active derivatives, cell lines stably expressing VEGF-D andits biologically active derivatives, and to a method of making apolypeptide using these expression vectors and host cells. The inventionalso relates to a method for treating and alleviating melanomas andvarious diseases.

Angiogenesis is a fundamental process required for normal growth anddevelopment of tissues, and involves the proliferation of newcapillaries from pre-existing blood vessels. Angiogenesis is not onlyinvolved in embryonic development and normal tissue growth, repair, andregeneration, but is also involved in the female reproductive cycle,establishment and maintenance of pregnancy, and in repair of wounds andfractures. In addition to angiogenesis which takes place in the normalindividual, angiogenic events are involved in a number of pathologicalprocesses, notably tumor growth and metastasis, and other conditions inwhich blood vessel proliferation, especially of the microvascularsystem, is increased, such as diabetic retinopathy, psoriasis andarthropathies. Inhibition of angiogenesis is useful in preventing oralleviating these pathological processes.

On the other hand, promotion of angiogenesis is desirable in situationswhere vascularization is to be established or extended, for exampleafter tissue or organ transplantation, or to stimulate establishment ofcollateral circulation in tissue infarction or arterial stenosis, suchas in coronary heart disease and thromboangitis obliterans.

Because of the crucial role of angiogenesis in so many physiological andpathological processes, factors involved in the control of angiogenesishave been intensively investigated. A number of growth factors have beenshown to be involved in the regulation of angiogenesis; these includefibroblast growth factors (FGFs), platelet-derived growth factor (PDGF),transforming growth factor alpha (TGFα), and hepatocyte growth factor(HGF). See, for example, Folkman et al., J. Biol. Chem., 1992 26710931-10934 for a review.

It has been suggested that a particular family of endothelialcell-specific growth factors and their corresponding receptors isprimarily responsible for stimulation of endothelial cell growth anddifferentiation, and for certain functions of the differentiated cells.These factors are members of the PDGF family, and appear to actprimarily via endothelial receptor tyrosine kinases (RTKs). Hithertoseveral vascular endothelial growth factor family members have beenidentified. Vascular endothelial growth factor (VEGF) is a homodimericglycoprotein that has been isolated from several sources. VEGF showshighly specific mitogenic activity against endothelial cells, and canstimulate the whole sequence of events leading to angiogenesis. Inaddition, it has strong chemoattractant activity towards monocytes, caninduce the plasminogen activator and the plasminogen activator inhibitorin endothelial cells, and can also influence microvascular permeability.Because of the latter activity, it is also sometimes referred to asvascular permeability factor (VPF). The isolation and properties of VEGFhave been reviewed; see Ferrara et al., J. Cellular Biochem., 1991 47211-218 and Connolly, J. Cellular Biochem., 1991 47 219-223.

More recently, six further members of the VEGF family have beenidentified. These are designated VEGF-B, described in InternationalPatent Application PCT/US96/02957 (WO 96/26736) and in U.S. Pat. Nos.5,840,693 and 5,607,918 by Ludwig Institute for Cancer Research and TheUniversity of Helsinki; VEGF-C, described in Joukov et al., The EMBOJournal, 1996 15 290-298; VEGF-D, described in International PatentApplication No. PCT/US97/14696 (WO 98/07832); the placenta growth factor(PlGF), described in Maglione et al., Proc. Natl. Acad. Sci. USA, 199188 9267-9271; VEGF2, described in International Patent Application No.PCT/US94/05291 (WO 95/24473) by Human Genome Sciences, Inc; and VEGF3,described in International Patent Application No. PCT/US95/07283 (WO96/39421) by Human Genome Sciences, Inc. Each show between 30% and 45%amino acid sequence identity with VEGF. The VEGF family members share aVEGF homology domain which contains the six cysteine residues which formthe cysteine knot motif. Functional characteristics of the VEGF familyinclude varying degrees of mitogenicity for endothelial cells, inductionof vascular permeability and angiogenic and lymphangiogenic properties.

VEGF-B has similar angiogenic and other properties to those of VEGF, butis distributed and expressed in tissues differently from VEGF. Inparticular, VEGF-B is very strongly expressed in heart, and only weaklyin lung, whereas the reverse is the case for VEGF. This suggests thatVEGF and VEGF-B, despite the fact that they are co-expressed in manytissues, may have functional differences.

VEGF-B was isolated using a yeast co-hybrid interaction trap screeningtechnique by screening for screening for cellular proteins which mightinteract with cellular retinoic acid-binding protein type I (CRABP-I).Its isolation and characteristics are described in detail inPCT/US96/02597 and in Olofsson et al., Proc. Natl. Acad. Sci. USA, 199693 2576-2581.

VEGF-C was isolated from conditioned media of PC-3 prostateadenocarcinoma cell line (CRL1435) by screening for ability of themedium to produce tyrosine phosphorylation of the endothelialcell-specific receptor tyrosine kinase VEGFR-3 (Flt4), using cellstransfected to express VEGFR-3. VEGF-C was purified using affinitychromatography with recombinant VEGFR-3, and was cloned from a PC-3 cDNAlibrary. Its isolation and characteristics are described in detail inJoukov et al., The EMBO Journal, 1996 15 290-298.

VEGF-D was isolated from a human breast cDNA library, commerciallyavailable from Clontech, by screening with an expressed sequence tagobtained from a human cDNA library designated “Soares Breast 3NbHBst” asa hybridization probe (Achen et al., Proc. Natl. Acad. Sci. USA, 1998 95548-553). Its isolation and characteristics are described in detail inInternational Patent Application No. PCT/US97/14696.

In PCT/US97/14696, the isolation of a biologically active fragment ofVEGF-D, designated VEGF-DΔNΔC, is also described. This fragment consistsof VEGF-D amino acid residues 93 to 201 of SEQ ID NO: 11 (whichcorresponds to SEQ ID NO: 5 of PCT/US97/14696) linked to the affinitytag peptide FLAG®. The entire disclosure of the International PatentApplication PCT/US97/14696 (WO 98/07832) is incorporated herein byreference.

VEGF-D has structural similarities to other members of the VEGF family.However, despite these structural similarities, it is structurally andfunctionally distinguished from other members of VEGF family. HumanVEGF-D is only 48% identical to VEGF-C, which is the member of thefamily to which VEGF-D is most closely related.

The VEGF-D gene is broadly expressed in the adult human, but iscertainly not ubiquitously expressed. VEGF-D is strongly expressed inheart, lung and skeletal muscle. Intermediate levels of VEGF-D areexpressed in spleen, ovary, small intestine and colon, and a lowerexpression occurs in kidney, pancreas, thymus, prostate and testis. NoVEGF-D mRNA was detected in RNA from brain, placenta, liver orperipheral blood leukocytes.

PlGF was isolated from a term placenta cDNA library. Its isolation andcharacteristics are described in detail in Maglione et al., Proc. Natl.Acad. Sci. USA, 1991 88 9267-9271. Presently its biological function isnot well understood.

VEGF2 was isolated from a highly tumorgenic, oestrogen-independent humanbreast cancer cell line. While this molecule is stated to have about 22%homology to PDGF and 30% homology to VEGF, the method of isolation ofthe gene encoding VEGF2 is unclear, and no characterization of thebiological activity is disclosed.

VEGF3 was isolated from a cDNA library derived from colon tissue. VEGF3is stated to have about 36% identity and 66% similarity to VEGF. Themethod of isolation of the gene encoding VEGF3 is unclear and nocharacterization of the biological activity is disclosed.

Vascular endothelial growth factors appear to act primarily by bindingto receptor tyrosine kinases. Five endothelial cell-specific receptortyrosine kinases have been identified, namely VEGFR-1 (Flt-1), VEGFR-2(KDR/Flk-1), VEGFR-3 (Flt4), Tie and Tek/Tie-2. All of these have theintrinsic tyrosine kinase activity which is necessary for signaltransduction. The essential, specific role in vasculogenesis andangiogenesis of VEGFR-1, VEGFR-2, VEGFR-3, Tie and Tek/Tie-2 has beendemonstrated by targeted mutations inactivating these receptors in mouseembryos.

The only receptor tyrosine kinases known to bind VEGFs are VEGFR-1,VEGFR-2 and VEGFR-3. VEGFR-1 and VEGFR-2 bind VEGF with high affinity,and VEGFR-1 also binds VEGF-B. VEGF-C has been shown to be the ligandfor VEGFR-3, and also activates VEGFR-2 (Joukov et al., The EMBOJournal, 1996 15 290-298). VEGF-D shares receptor specificity withVEGF-C (Achen et al., Proc. Natl. Acad. Sci. USA, 1998 95 548-553). Aligand for Tek/Tie-2 has been described (International PatentApplication PCT/US95/12935 (WO 96/11269) by Regeneron Pharmaceuticals,Inc.); however, the ligand for Tie has not yet been identified.

The primary translation products of VEGF-D and VEGF-C have long -andC-terminal polypeptide extensions in addition to a central VEGF homologydomain (VHD). In the case of VEGF-C, these polypeptide extensions arepropeptides which are proteolytically cleaved to generate a secretedform which consists only of the VHD and is capable of binding to VEGFR-2and VEGFR-3 (Joukov et al., The EMBO Journal, 1996 15 290-298; Joukov etal., EMBO J., 1997 16 3898-3911). Likewise, a recombinant form ofVEGF-D, consisting only of the VHD, was shown to bind and activate thesereceptors and to be mitogenic for endothelial cells, although VEGF-Dprocessing was uncharacterized (Achen et al., Proc. Natl. Acad. Sci.USA, 1998 95 548-553).

Recently, a novel 130-135 kDa VEGF-A isoform specific receptor has beenpurified and cloned (Soker et al., Cell, 1998 92 735-745). The VEGFreceptor was found to bind specifically the VEGF-A₁₆₅ isoform via theexon 7 encoded sequence, which shows weak affinity for heparin (Soker etal., Cell, 1998 92 735-745). Surprisingly, the receptor was shown to beidentical to human neuropilin-1 (NP-1), a receptor involved in earlystage neuromorphogenesis. PlGF-2 also appears to interact with NP-1(Migdal et al., J. Biol. Chem., 1998 273 22272-22278).

Gene targeting studies have demonstrated the absolute requirement ofVEGFR-1, VEGFR-2 and VEGFR-3 for embryonic development. These studiesshow that VEGFR-1 plays a role in vascular endothelial tube formation,VEGFR-2 is important for endothelial/hematopoietic cell differentiationand mitogenesis, and VEGFR-3 is involved in regulation of vascularremodeling, the formation of large vessels and in lymphangiogenesis. Thefunctions of these receptors are reviewed in Mustonen and Alitalo, J.Cell Biol., 1995 129 895-898.

The VEGFR-3 is expressed in venous and lymphatic endothelia in thefetus, and predominantly in lymphatic endothelia in the adult (Kaipainenet al., Cancer Res, 1994 54 6571-6577; Proc. Natl. Acad. Sci. USA, 199592 3566-3570). VEGFR-3 has an essential role in the development of theembryonic cardiovascular system before the emergence of the lymphaticvessels (Dumont et al., Science, 1998 282 946-949). It has beensuggested that VEGF-C may have a primary function in lymphaticendothelium, and a secondary function in angiogenesis and permeabilityregulation which is shared with VEGF (Joukov et al., The EMBO Journal,1996 290-298).

SUMMARY OF THE INVENTION

The invention generally provides expression vectors comprising VEGF-Dand its biologically active derivatives, cell lines stably expressingVEGF-D and its biologically active derivatives, and a method of making apolypeptide using these expression vectors and host cells. The inventionalso generally provides for a method for treating and alleviatingmelanomas or tumors expressing VEGF-D and various diseases.

According to a first aspect, the present invention provides a mammaliancell line stably expressing VEGF-D or a fragment or analog thereofhaving the biological activity of VEGF-D. Optionally VEGF-D produced bythe cell line of the invention is linked to an epitope tag such as FLAG®(SEQ ID NO: 16), hexahistidine or I-SPY™ to assist in affinitypurification and in localization of VEGF-D. Preferably the mammaliancell line is the 293-EBNA human embryonal kidney cell line. Preferablythe VEGF-D expressed is VEGF-DFullNFlag, VEGF-DFulCFlag, VEGF-DΔNΔC, orVEGF-DΔC, as described herein.

The expression “biological activity of VEGF-D” is to be understood tomean the ability to stimulate one or more of endothelial cellproliferation, differentiation, migration, survival or vascularpermeability.

A preferred fragment of VEGF-D is the portion of VEGF-D from amino acidresidue 93 to amino acid residue 201 (i.e. the VEGF homology domain(VHD)) (SEQ ID NO:1) of SEQ ID NO: 11 (which corresponds to SEQ ID NO: 5of PCT/US97/146961 optionally linked to the FLAG® peptide. Where thefragment is linked to FLAG®, the fragment is referred to herein asVEGF-DΔNΔC.

As used herein, the term “VEGF-D” collectively refers to any of thepolypeptides of SEQ ID NOs: 11, 12, 13 and 14 (which correspond to SEQID NOs: 5, 3, 8 and 9, respectively, as defined in International PatentApplication PCT/US97/14696), and SEQ ID NO: 15, which corresponds toamino acid residues 93 to 201 of SEQ ID NO: 14, and fragments or analogsthereof which have the biological activity of VEGF-D as herein defined.

According to a second aspect, the invention provides an expressionvector comprising a sequence of human cDNA encoding VEGF-D, insertedinto the mammalian expression vector Apex-3. Preferably the expressionvector is pVDApexFullNFlag, VEGF-DFullCFlag, pVDApexΔNΔC or pVDApexΔC,as described herein.

Preferably the expression vector also comprises a sequence encoding anaffinity tag such as FLAG®, hexahistidine or I-SPY™.

The invention further provides a method of making a polypeptideaccording to the invention, comprising the steps of expressing anexpression vector of the invention in a host cell, and isolating thepolypeptide from the host cell or from the host cell's growth medium. Inone preferred embodiment of this aspect of the invention, the expressionvector further comprises a sequence encoding an affinity tag, such asFLAG®, hexahistidine or I-SPY™, in order to facilitate purification ofthe polypeptide by affinity chromatography.

The polypeptides comprising conservative substitutions, insertions ordeletions but which still retain the biological activity of VEGF-D areclearly to be understood to be within the scope of the invention.Persons skilled in the art will be well aware of the methods which canbe readily used to generate such polypeptides, for example the use ofsite-directed mutagenesis, or specific enzymatic cleavage and ligation.The skilled person will also be aware that peptidomimetic compounds orcompounds in which one or more amino acid residues are replaced by anon-naturally occurring amino acid or an amino acid analog may retainthe required aspects of the biological activity of VEGF-D. Suchcompounds can be readily made and tested by methods known in the art,and are also within the scope of the invention.

In addition, variant forms of the VEGF-D polypeptide which result fromalternative splicing, as are known to occur with VEGF and VEGF-B, andnaturally-occurring allelic variants of the nucleic acid sequenceencoding VEGF-D are encompassed within the scope of the invention.Allelic variants are well known in the art, and represent alternativeforms of the encoded polypeptide.

Such variant forms of VEGF-D can be prepared by targeting non-essentialregions of the VEGF-D polypeptide for modification. These non-essentialregions are expected to fall outside the strongly-conserved regions. Inparticular, the growth factors of the PDGF family, including VEGF, aredimeric, and VEGF, VEGF-B, VEGF-C, VEGF-D, PDGF-A and PDGF-B showcomplete conservation of eight cysteine residues in the PDGF-likedomains (Olofsson et al., Proc. Natl. Acad. Sci. USA, 1996 93 2576-2581;Joukov et al., The EMBO Journal, 1996 15 290-298). These cysteines arethought to be involved in intra- and inter-molecular disulfide bonding.Loops 1, 2 and 3 of each subunit, which are formed by intra-moleculardisulfide bonding, are involved in binding to the receptors for thePDGF/VEGF family of growth factors (Andersson et al., Growth Factors,1995 12 159-164). As noted above, the cysteines conserved in previouslyknown members of the VEGF family are also conserved in VEGF-D.

Persons skilled in the art thus are well aware that these cysteineresidues should be preserved in any proposed variant form, and that theactive sites present in loops 1, 2 and 3 also should be preserved.However, other regions of the molecule can be expected to be of lesserimportance for biological function, and therefore offer suitable targetsfor modification. Modified polypeptides can be readily tested for theirability to show the biological activity of VEGF-D by routine activityassay procedures such as cell proliferation tests.

It is contemplated that some modified VEGF-D polypeptides will have theability to bind to endothelial cells, i.e. to VEGF-D receptors, but willbe unable to stimulate endothelial cell proliferation, differentiation,migration or survival, or induce vascular permeability. These modifiedpolypeptides are expected to be able to act as competitive ornon-competitive inhibitors of VEGF-D, and to be useful in situationswhere prevention or reduction of VEGF-D action is desirable. Thus suchreceptor-binding but non-mitogenic, non-differentiation inducing,non-migration inducing or non-survival promoting variants of VEGF-D arealso within the scope of the invention, and are referred to herein as“receptor-binding but otherwise inactive or interfering variants”.

Likewise, it is contemplated that some modified VEGF-D polypeptides willhave the ability to bind VEGF-D and will prevent binding of the dimer toVEGF-D receptors (e.g. VEGFR-2 and VEGFR-3) on endothelial cells. Thusthese diners will be unable to stimulate endothelial cell proliferation,differentiation, migration or survival, or induce vascular permeability.These modified polypeptides are expected to be able to act ascompetitive or non-competitive inhibitors of VEGF-D, and to be useful insituations where prevention or reduction of VEGF-D action is desirable.Thus such VEGF-D-binding but non-mitogenic, non-differentiationinducing, non-migration inducing or non-survival promoting variants ofVEGF-D are also within the scope of the invention, and are referred toherein as “VEGF-D-binding but otherwise inactive or interferingvariants”.

According to a third aspect, the invention provides a method oftreatment or alleviation of malignant melanoma or tumors expressingVEGF-D, comprising the step of inhibiting the expression or activity ofVEGF-D in the vicinity of the melanoma or tumor. Local inhibition ofVEGF-D expression may be achieved for example by the use of anti-sensenucleic acid or triple-stranded DNA encoding VEGF-D. Alternatively aVEGF-D variant polypeptide, as described above, which has the ability tobind to VEGF-D and prevent binding to the VEGF-D receptors or which bindto the VEGF-D receptors, but which is unable to stimulate endothelialcell proliferation, differentiation, migration or survival may be usedas a competitive or non-competitive inhibitor of VEGF-D. Small moleculeinhibitors to VEGF-D, VEGFR-2 or VEGFR-3 and antibodies directed againstVEGF-D, VEGFR-2 or VEGFR-3 may also be used.

Use of the above method is also contemplated in non-malignantconditions, where there is increased or continuous expression of VEGF-D,such as in psoriasis. Based on the distribution of VEGF-D in the skin ofthe developing mouse embryo it is possible that VEGF-D plays a role inthe initiation or continuation of high epidermal cell turnoverdermatoses such as psoriasis, where vascular proliferation in the upperdermis is a consistent and prominent histopathological feature.

In an additional aspect of the invention, VEGF-D is conjugated to toxinsor drugs which have endothelial cell inhibiting activity that would betargeted to proliferating vascular and lymphatic endothelial cells whichexpress VEGF-D receptors, e.g. VEGFR-2 and VEGFR-3. Thus, growth ofvessels, which is important for numerous pathological conditions, suchas tumor growth, could be blocked.

According to a fifth aspect, the invention provides a method ofenhancing the acceptance and/or healing of a skin graft, comprising thestep of stimulating angiogenesis and lymphangiogenesis with an effectivedose of VEGF-D, or a fragment or analog thereof having the biologicalactivity of VEGF-D.

According to a sixth aspect, the invention provides a method ofstimulating the healing of a surgical or traumatic wound to the skin,comprising the step of stimulating angiogenesis and lymphangiogenesiswith an effective dose of VEGF-D, or a fragment or analog thereof havingthe biological activity of VEGF-D.

It is contemplated that the latter two aspects of the invention will beparticularly useful in the treatment of burns and in plastic surgery.

In another aspect of the invention a method is provided for stimulatinglymphangiogenesis for treatment or alleviation of lymphedema, comprisingthe step of stimulating lymphangiogenesis with an effective dose ofVEGF-D, or a fragment or analog thereof having the biological activityof VEGF-D. Few diseases are as disfiguring as lymphedema. Lymphedemaoccurs when there is obstruction of the lymphatic vessels which areinvolved in the draining of fluid bathing the tissues. As a result ofthis obstruction, lymph or fatty fluid accumulates within the tissuesand results in limb and tissue engorgement. The end result is oftengrotesque and severely incapacitating due to local infections,discomfort and deformity. There are several causes of lymphedema. Mostnotable is breast cancer associated with either lymph node obstructionor removal during surgery. Recurrent infections and other forms ofsurgery are also associated with lymphedema. A significant proportion ofpatients with lymphedema have no identifiable precitant. Increasing theamount of VEGF-D should induce lymphangiogenesis and alleviate lymph andfatty fluid accumulation.

Inappropriate down-regulation of VEGF-D synthesis during embryogenesismay also be important in adnexal structure maldevelopment includinganhydrotic ectodermal dysplasia. Normally the sweat glands in the dermisare surrounded by vascularized fatty connective tissue. If the vascularsupply is compromised or unable to replenish due to a possible lack ofVEGF-D, it will lead to sweat gland hypoxia and malfunction. Theselesions may be due to lack of ability of differentiated cells at somestage of development to produce VEGF-D or production of blocking agentsto the VEGF-D receptors on blood vessels adjacent to differentiatingadnexal cells producing such blocking agents. Thus the inventionprovides a method for treating or alleviating anhydrotic ectodermaldysplasia by stimulating vascularization of fatty connective tissue,comprising the step of administering an effective dose of VEGF-D, or afragment or analog thereof having the biological activity of VEGF-D.

A further disease which may be related to a lack of VEGF-D or lack ofresponse to VEGF-D is scleroderma. Scleroderma is an uncommon disorderof connective tissue characterized by thickening and increasedcollagenization of the skin that is thought to be due to changes invascularization and/or fibroblast function. Damage to the endothelialcells due to a lack of VEGF-D or to a failure to response to VEGF-D maybe a contributing factor to the inability of the vessels to repairleading to the continued platelet aggregation observed and subsequentrelease of growth factors having a mitogenic action on fibroblasts. Thisresults in increased collagen production. The same considerations applyto systemic organ involvement in scleroderma. Thus the inventionprovides a method for treating or alleviating scleroderma by stimulatingproliferation of vascular endothelial cells, comprising the step ofadministering an effective dose of VEGF-D, or a fragment or analogthereof having the biological activity of VEGF-D.

According to a seventh aspect, the invention provides a method forstimulating at least one bioactivity of VEGF-D selected from endothelialcell proliferation, migration, survival and differentiation, andlymphangiogenesis without inducing vascular permeability, comprising thestep of administering a bioactivity stimulating amount of fullyprocessed VEGF-D.

A further aspect of the invention provides a method for regulatingreceptor-binding specificity of VEGF-D, comprising the steps ofexpressing an expression vector comprising a nucleotide sequenceencoding an unprocessed VEGF-D and supplying a proteolytic amount of atleast one enzyme for processing the encoded VEGF-D to generate aproteolytically processed form of VEGF-D.

It will be clearly understood that for the purposes of thisspecification the phrase “fully processed VEGF-D” means a VEGF-Dpolypeptide without the N- and C-terminal propeptides, the phrase“proteolytically processed form of VEGF-D” means a VEGF-D polypeptidewithout the N- and/or C-terminal propeptide, and the phrase “unprocessedVEGF-D” means a VEGF-D polypeptide with both the N- and C-terminalpropeptides.

The invention also provides a method of detecting tumors expressingVEGF-D in a biological sample, comprising the steps of contacting saidsample with a specific binding reagent for VEGF-D, allowing time for abinding of said specific binding reagent to VEGF-D, and detecting saidbinding. In a preferred embodiment the specific binding reagent forVEGF-D is an antibody and the binding and/or extent of binding isdetected by means of an antibody with a detectable label. Quantitationof VEGF-D in cancer biopsy specimens will be useful as an indicator offuture metastatic risk.

Antibodies according to the invention may be labeled with a detectablelabel, and utilized for diagnostic purposes. The antibody may becovalently or non-covalently coupled to a suitable supermagnetic,paramagnetic, electron dense, ecogenic or radioactive agent for imaging.For use in diagnostic assays, radioactive or non-radioactive labels maybe used. Examples of radioactive labels include a radioactive atom orgroup, such as .sup.125I or .sup.32P. Examples of non-radioactive labelsinclude enzyme labels, such as horseradish peroxidase, or fluorimetriclabels, such as fluorescein-5-isothiocyanate (FITC). Labeling may bedirect or indirect, covalent or non-covalent.

The polypeptides or antibodies which induce the biological activity ofVEGF-D may be employed in combination with a suitable pharmaceuticalcarrier. The polypeptides, VEGF-D antagonists or antibodies whichinhibit the biological activity of VEGF-D also may be employed incombination with a suitable pharmaceutical carrier. Such compositionscomprise a therapeutically effective amount of the antibody, and apharmaceutically acceptable carrier or adjuvant. Examples of such acarrier include, but are not limited to, saline, buffered saline,mineral oil, talc, dextrose, water, glycerol, ethanol, thickeners,stabilizers, suspending agents and combinations thereof. Suchcompositions may be in the form of solutions, suspensions, tablets,capsules, creams, salves, ointments or other conventional forms. Theformulation is selected to suit the mode of administration. Wherepolypeptides, VEGF-D antagonists or antibodies are to be used fortherapeutic purposes, the dose and route of application will depend uponthe nature of the patient and condition to be treated, and will be atthe discretion of the attending physician or veterinarian. Suitableroutes include subcutaneous, intramuscular, intraperitoneal orintravenous injection, topical application, implants etc. Topicalapplication of VEGF-D may be used in a manner analogous to VEGF.

It will be clearly understood that for the purposes of thisspecification the word “comprising” means “including but not limitedto”. The corresponding meaning applies to the word “comprises”.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematic maps of the Apex-3 plasmid constructs forexpression of human VEGF-D derivatives in 293-EBNA cells;

FIG. 2 shows the expression of VEGF-D derivatives by 293-EBNA cells;

FIG. 3 shows the precipitation of VEGF-D by soluble VEGFreceptor-immunoglobulin fusion proteins;

FIG. 4 shows the nucleotide sequence of a cDNA encoding mouse VEGF-D1(SEQ ID NO:2), isolated by hybridization screening from acommercially-available mouse lung cDNA library;

FIGS. 5A and 5B show autoradiographs taken after two days of exposure tomouse 15.5 days post-coital tissue sections hybridized with VEGF-Dantisense (FIG. 5A) and sense (FIG. 5B) RNAs;

FIGS. 6A-6D show the results of analysis of the distribution of VEGF-DmRNA in the post-coital day 15.5 mouse embryo by in situ hybridization;

FIGS. 7A-7E show the analysis of human malignant melanoma byimmunohistochemistry with VEGF-D monoclonal antibodies;

FIG. 8 provides a schematic representation of the structural domains ofVEGF-D and some VEGF-D derivatives

FIGS. 9A-9E show the analyses of VEGF-D derivatives secreted by 293-EBNAcells expressing VEGF-DFullNFlag (FIGS. 9A, 9B and 9C) and VEGF-DΔC(FIGS. 9D and 9E);

FIGS. 10A and 10B show the analysis of VEGF-DΔNΔC by size exclusionchromatography and SDS-PAGE; and

FIG. 11 provides a schematic representation of the mode of VEGF-Dprocessing.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Example 1 Cell LinesStably Expressing VEGF-D Derivatives

In order to generate cell lines constitutively expressing derivatives ofVEGF-D, regions of the human VEGF-D cDNA were inserted into themammalian expression vector Apex-3 (Evans et al, Mol. Immunol., 1995 321183-1195). This vector is maintained episomally when transfected into293-EBNA human embryonal kidney cells. For expression of VEGF-DΔNΔC, ADNA fragment encoding residues 93 to 201 (SEQ ID NO:1) was amplified bypolymerase chain reaction (PCR) with Pfu DNA polymerase, using astemplate a plasmid comprising full length VEGF-D cDNA (SEQ ID NO: 10).The amplified DNA fragment, the correctness of which was confirmed bynucleotide sequencing, was then inserted into the expression vectorpEFBOSSFLAG (a gift from Dr. Clare McFarlane at the Walter and ElizaHall Institute for Medical Research (WEHI), Melbourne, Australia, asdescribed in Evans, et al., J. Immunol. Methods, 184:123-135 (1995)), togive rise to a plasmid designated pEFBOSVEGF-DΔNΔC. The pEFBOSVEGF-DΔNΔCvector contains DNA encoding the signal sequence for protein secretionfrom the interleukin-13 (IL-3) gene and the FLAG® octapeptide (SigmaAldrich). The FLAG® octapeptide can be recognized by commerciallyavailable antibodies such as the M2 monoclonal antibody (Sigma Aldrich).The VEGF-D PCR fragment was inserted into the vector such that the IL-3signal sequence was immediately upstream from the FLAG® octapeptide,which was in turn immediately upstream from the truncated VEGF-Dsequence. All three sequences were in the same reading frame, so thattranslation of mRNA resulting from transfection of pEFBOSVEGF-DΔNΔC intomammalian cells would give rise to a protein which would have the IL-3signal sequence at its N-terminus, followed by the FLAG® octapeptide andthe truncated VEGF-D sequence. Cleavage of the signal sequence andsubsequent secretion of the protein from the cell would give rise to aVEGF-D polypeptide which is tagged with the FLAG® octapeptide adjacentto the N-terminus. The region of pEFBOSVEGF-DΔNΔC containing thesequence encoding the IL-3 signal sequence, the FLAG® octapeptide andthe DNA fragment encoding residues 93 to 201 of VEGF-D (SEQ ID NO:1) wasinserted into the XbaI site of Apex-3. The resulting plasmid wasdesignated pVDApexΔNΔC, and is illustrated schematically in FIG. 1.

In addition, a second plasmid was constructed, designatedpEFBOSVEGFDfullFLAG, in which the full length coding sequence of humanVEGF-D (SEQ ID NO: 10) was inserted into EFBOSIFLAG such that thesequence for the FLAG® octapeptide was immediately downstream from, andin the same reading frame as, the coding sequence of VEGF-D. The plasmidpEFBOSIFLAG lacks the IL-3 signal sequence, so secretion of theVEGF-D/FLAG fusion protein was driven by the signal sequence of VEGF-D.pEFBOSVEGFDfullFLAG was designed to drive expression in mammalian cellsof full-length VEGF-D which was C-terminally tagged with the FLAG®octapeptide. This protein is designated VEGFDfullCFLAG. The resultingplasmid was designated pVDApexΔNΔC, and is illustrated schematically inFIG. 1.

Similar types of constructs were made for expression of VEGF-DFullNFlag,a derivative of full-length human VEGF-D (SEQ ID NO: 11) which had beentagged with FLAG® at the N-terminus, and for expression of a truncatedderivative of human VEGF-D, consisting of amino acid residues 2 to 202(SEQ ID NO: 11), designated VEGF-DΔC. The expression constructs forthese VEGF-D derivatives were designated pVDApexFullNFlag and pVDApexΔCrespectively, and are also shown schematically in FIG. 1. IL-3 SSdenotes the interleukin-3 signal sequence, and the arrows indicate thedirection of transcription proceeding from the cytomegalovirus promoter(CMV) through the expression cassettes. These vectors were transfectedinto cells of the human embryo kidney cell line 293-EBNA by the calciumphosphate method, and stable transfectants were selected in the presenceof hygromycin. Cell lines expressing high levels of VEGF-DFullNFlag,VEGF-DΔC and VEGF-DΔNΔC were subsequently identified by metaboliclabeling, immunoprecipitation and Western blot analysis, as shown inFIG. 2.

In FIG. 2, the 293-EBNA cell lines expressing VEGF-DFullNFlag,VEGF-DΔNΔC and VEGF-DΔC were metabolically labeled, and proteins inconditioned medium samples were immunoprecipitated with anti-FLAGantibody (M2) or with antiserum specific for the VEGF homology domain ofVEGF-D (A2). The precipitated proteins were analyzed by SDS-PAGE andvisualized by autoradiography in the case of VEGF-DFullNFlag andVEGF-DΔNΔC or detected in Western blot analysis with M2 antibody in thecase of VEGF-DΔC. Arrows denote the positions of VEGF-D derivatives.These derivatives were not detected from control supernatants derivedfrom parental 293-EBNA cells (data not shown). The positions ofmolecular weight markers (in kDa), are shown to the right of each panel.The band at approximately 50 kDa detected by Western blot analysis ofVEGF-DΔC corresponds to the immunoglobulin heavy chain.

Numerous VEGF-D derivatives were detected in the supernatants of cellsexpressing VEGF-DFullNFlag and VEGF-DΔC. These derivatives are formed asa result of proteolytic processing which occurs as part of thebiosynthesis of VEGF-D. The cell lines expressing VEGF-DNFullFlag,VEGF-DΔC and VEGF-DΔNΔC have been maintained under hygromycin selectionwhile being passaged at least twenty times, and continue to express theVEGF-D derivatives.

Example 2 Binding of VEGF-DΔNΔC to Soluble VEGF Receptors

To further assess the interactions between VEGF-D and the VEGFreceptors, VEGF-DΔNΔC was tested for its capacity to bind to solubleimmunoglobulin fusion proteins comprising the extracellular domains ofhuman VEGFR-1, human VEGFR-2 and human VEGFR-3. The correspondingfragment of VEGF-C, VEGF-CΔNΔC, was used for comparison. For bindingexperiments, 293T human embryonal kidney cells were transfected withplasmids encoding the soluble receptor-immunoglobulin fusion proteinsVEGFR-1-Ig, VEGFR-2-Ig or VEGFR-3-Ig using the calcium-phosphate(Ca-phosphate) method. In these fusion proteins, the extracellulardomain of the relevant VEGF receptor is fused to the Fc portion of humanIgG.sub.1. The cells were incubated for 24 hours after transfection,washed with Dulbecco's Modified Eagle's Medium (DMEM) containing 0.2%bovine serum albumin (BSA) and starved for 24 hours. Media were thencollected and clarified by centrifugation, and fusion proteins wereprecipitated using protein A Sepharose beads. The Sepharose beads werethen incubated at room temperature for 3 hours with 900 μl ofmetabolically .sup.35S-labeled medium from 293-EBNA cells which had beentransfected with expression plasmids encoding human VEGF-DΔNΔC, humanVEGF-CΔNΔC or human VEGF.sub.15 using the Ca-phosphate method. Metaboliclabeling of 293-EBNA cells was carried out essentially as described(Joukov et al., 1997). The Sepharose beads were then washed twice withbinding buffer (0.5% BSA, 0.02% Tween 20, 1 μg/ml heparin in phosphatebuffered saline (PBS)) at 4.degree. C. and once with PBS, boiled inLaemmli sample buffer, and proteins were then analyzed by SDS-PAGE. Theresults are shown in FIG. 3.

In FIG. 3, precipitation of labeled VEGF₁₆₅, VEGF-CΔNΔC and VEGF-DΔNΔCby VEGFR-1-Ig, VEGFR-2-Ig and VEGFR-3-Ig was carried out as describedabove. The fusion proteins used for the precipitations are shown to theright. “Vector” denotes results of precipitations from medium derivedfrom cells transfected with expression vector lacking sequence encodingthe VEGFs. The molecular weight markers are indicated in kDa

A polypeptide of the size expected for VEGF-DΔNΔC (approximately 22 kDa)was precipitated by VEGFR-2-Ig and VEGFR-3-Ig from the medium of cellsexpressing VEGF-DΔNΔC. In contrast, no protein of this size wasprecipitated from the same medium by VEGFR-1-Ig. Essentially the sameresults were observed for precipitation of VEGF-CΔNΔC. As expected, apredominant polypeptide of approximately 24 kDa was precipitated byVEGFR-1-Ig and VEGFR-2-Ig from the medium of cells expressing VEGF₁₆₅,but was not precipitated by VEGFR-3-Ig. No labeled polypeptides wereprecipitated by the three fusion proteins from the medium of cellstransfected with the expression vector lacking sequences encoding theVEGFs. These data indicate that VEGF-DΔNΔC can bind to VEGFR-2 andVEGFR-3 but not to VEGFR-1. Thus VEGF-DΔNΔC resembles VEGF-CΔNΔC in thereceptor-binding specificity to VEGFR-2 and VEGFR-3.

Example 3 In Situ Hybridization Studies of VEGF-D Gene Expression inMouse Embryos

The pattern of VEGF-D gene expression was studied by in situhybridization using a radiolabeled antisense RNA probe corresponding tonucleotides 1 to 340 of the mouse VEGF-D1 cDNA, whose sequence is shownin FIG. 4. The antisense RNA was synthesized by in vitro transcriptionwith T3 RNA polymerase and [³⁵S] UTPαs. Mouse VEGF-D is fully describedin International Patent application PCT/US97/14696. This antisense RNAprobe was hybridized to paraffin-embedded tissue sections of mouseembryos at post-coital day 15.5. The labeled sections were subjected toautoradiography for 2 days. The resulting autoradiographs for sectionshybridized to the antisense RNA and to complementary sense RNA (asnegative control) are shown in FIG. 5A-B. In FIG. 5A, “L” denotes lungand “Sk” denotes skin, and the two tissue sections shown are serialsections. Strong signals for VEGF-D mRNA were detected in the developinglung and associated with the skin. No signals were detected using thecontrol sense RNA (FIG. 5B).

In FIGS. 6A-D, sagittal tissue sections were hybridized with VEGF-Dantisense RNA probe and subsequently incubated with photographicemulsion, developed and stained. Microscopic analysis revealed thatVEGF-D mRNA was abundant in the mesenchymal cells of the developing lung(FIG. 6A-C). In contrast, the epithelial cells of the bronchi andbronchioles were negative, as were the developing smooth muscle cellssurrounding the bronchi. The endothelial cells of bronchial arterieswere also negative. In FIG. 6A, the dark field micrograph shows a strongsignal for VEGF-D mRNA in lung (Lu). Liver (Li) and ribs (R) are alsoshown. FIG. 6B shows a higher magnification of the lung. The light fieldmicrograph shows a bronchus (Br) and bronchial artery (BA). The blackoutline of a rectangle denotes the region of the section shown in FIG.6C but at a higher magnification. FIG. 6C shows the epithelial cells ofthe bronchus (Ep), the developing smooth muscle cells (SM) surroundingthe epithelial cell layer and the mesenchymal cells (Mes). The abundanceof silver grains associated with mesenchymal cells is apparent. In FIG.6D, a dark field micrograph shows a limb bud. A strong signal waslocated immediately under the skin in a region of tissue rich infibroblasts and developing melanocytes. The magnification for FIGS. 6Aand D is ×40, for FIG. 6B, it is ×200 and for FIG. 6C, it is ×500.

The results presented here suggest that VEGF-D may attract the growth ofblood and lymphatic vessels into the developing lung and into the regionimmediately underneath the skin. Due to the expression of the VEGF-Dgene adjacent to the skin, it is considered that VEGF-D could play arole in inducing the angiogenesis that is associated with malignantmelanoma. Malignant melanoma is a very highly vascularized tumor. Thissuggests that local inhibition of VEGF-D expression, for example usingVEGF-D or VEGF receptor-2 or VEGF receptor-3 antibodies, is useful inthe treatment of malignant melanoma. Other suitable inhibitors of VEGF-Dactivity, such as anti-sense nucleic acids or triple-stranded DNA, mayalso be used.

Example 4 Production of Monoclonal Antibodies that Bind to Human VEGF-D

Monoclonal antibodies to VEGF-DΔNΔC were raised in mice. VEGF-DΔNΔCincludes the amino acid sequence of the VHD of VEGF-D and is similar insequence to all other members of the VEGF family. Therefore, it isthought that the bioactive portion of VEGF-D likely resides in the VHD.A DNA fragment encoding a truncated portion of human VEGF-D from residue93 to 201, i.e. with the N- and C-terminal regions removed, wasamplified by polymerase chain reaction (PCR) with Pfu DNA polymerase,using as template a plasmid comprising full-length human VEGF-D cDNA.The amplified DNA fragment, the sequence of which was confirmed bynucleotide sequencing, was then inserted into the expression vectorpEFBOSSFLAG (a gift from Dr. Clare McFarlane at the Walter and ElizaHall Institute for Medical Research (WEHI), Melbourne, Australia) togive rise to a plasmid designated pEFBOSVEGF-DΔNΔC. The pEFBOSSFLAGvector contains DNA encoding the signal sequence for protein secretionfrom the interleukin-3 (IL-3) gene and the FLAG® octapeptide(Sigma-Aldrich). The FLAG® octapeptide can be recognized by commerciallyavailable antibodies such as the M2 monoclonal antibody (Sigma-Aldrich).The VEGF-D PCR fragment was inserted into the vector such that the IL-3signal sequence was immediately upstream from the FLAG® octapeptide,which was in turn immediately upstream from the truncated VEGF-Dsequence. All three sequences were in the same reading frame, so thattranslation of mRNA resulting from transfection of pEFBOSVEGF-DΔNΔC intomammalian cells would give rise to a protein which would have the IL-3signal sequence at its N-terminus, followed by the FLAG® octapeptide andthe truncated VEGF-D sequence. Cleavage of the signal sequence andsubsequent secretion of the protein from the cell would give rise to aVEGF-D polypeptide which is tagged with the FLAG® octapeptide adjacentto the N-terminus. This protein was designated VEGF-DΔNΔC. VEGF-DΔNΔCwas purified by anti-FLAG® affinity chromatography from the medium ofCOS cells which had been transiently transfected with the plasmidpEFBOSVEGF-DΔNΔC. (see Example 9 in International Patent Application No.PCT/US97/14696).

Purified VEGF-DΔNΔC was used to immunize female Balb/C mice on day 85(intraperitoneal), 71 (intraperitoneal) and 4 (intravenous) prior to theharvesting of the spleen cells from the immunized mice and subsequentfusion of these spleen cells to mouse myeloma P3X63Ag8.653 (NS-1) cells.For the first two immunizations, approximately 10 μg of VEGF-DΔNΔC in a1:1 mixture of PBS and TiterMax adjuvant (#R-1 Research adjuvant; CytRxCorp., Norcross, Ga.) were injected, whereas for the third immunization35 μg of VEGF-DΔNΔC in PBS was used.

Monoclonal antibodies to VEGF-DΔNΔC were selected by screening thehybridomas on purified VEGF-DΔNΔC using an enzyme immunoassay. Briefly,96-well microtiter plates were coated with VEGF-DΔNΔC, and hybridomasupernatants were added and incubated for 2 hours at 4° C., followed bysix washes in PBS with 0.02% Tween 20. Incubation with a horse radishperoxidase conjugated anti-mouse Ig (Bio-Rad, Hercules, Calif.) followedfor 1 hour at 4° C. After washing, the assay was developed with an2,2′-azino-di-(3-ethylbenz-thiazoline sulfonic acid) (ABTS) substratesystem (Zymed, San Francisco, Calif.), and the assay was quantified byreading absorbance at 405 nm in a multiwell plate reader (FlowLaboratories MCC/340, McLean, Va.) Six antibodies were selected forfurther analysis and were subcloned twice by limiting dilution. Theseantibodies were designated 2F8, 3C10, 4A5, 4E10, 4H4 and 5F12. Theisotypes of the antibodies were determined using an Isostrip™ isotypingkit (Boehringer Mannheim, Indianapolis, Ind.) Antibodies 2F8, 4A5, 4E10and 5F12 were of the IgG.sub.I class whereas 4H4 and 3C10 were of theIgM class. All six antibodies contained the kappa light chain.

Hybridoma cell lines were grown in DMEM containing 5% v/v IgG-depletedserum (Gibco BRL, Gaithersburg, Md.), 5 mM L-glutamine, 50 μg/mlgentamicin and 10 μg/ml recombinant IL-6. Antibodies 2F8, 4A5, 4E10 and5F12 were purified by affinity chromatography using protein G-Sepharoseaccording to the technique of Darby et al., J. Immunol. Methods, 1993159 125-129, and the yield assessed by measuring absorption at 280 nm.

Example 5 Use of Monoclonal Antibodies to Human VEGF-D forImmunohistochemical Analysis of Human Tumors

In order to assess the role of VEGF-D in tumorigenesis, the abovedescribed MAbs were used for immunohistochemical analysis of a humanmalignant melanoma. Four VEGF-D MAbs, 2F8, SF12, 4A5 and 4E10, were usedfor the analysis. A MAb raised to the receptor for granulocytecolony-stimulating factor, designated LMM774 (Layton et al., GrowthFactors, 1997 14 117-130), was used as a negative control. Like theVEGF-D MAbs, LMM774 was of the mouse IgG₁ isotype and therefore servedas an isotype-matched control antibody. The MAbs were tested against tworandomly chosen invasive malignant melanomas by immunohistochemistry.Five micrometer thick sections from formalin fixed and paraffin embeddedtissue of the cutaneous malignant melanomas were used as the testtissue. The sections were dewaxed and rehydrated and then washed withPBS. Normal rabbit serum diluted 1:50 was applied to each section for 20minutes. The excess serum was blotted off and the primary antibodies,i.e. the VEGF-D MAbs and LMM774 at crudely optimized dilutions of 1:100and 1:200, were applied to the sections and incubated in a moist chamberat room temperature overnight. The sections were again washed in PBS for5 minutes followed by the application of biotinylated rabbit anti-mouseantibodies (DAKO Corp., Carpinteria, Calif.) at a 1:400 dilution in PBSfor 35 minutes at room temperature. The sections were then washed intris buffered saline (TBS) for 5 minutes and then streptavidin-alkalinephosphatase (Silenus, Australia) was applied at a 1:500 dilution in TBS.The sections were washed in TBS for 5 minutes and the fast red substrate(Sigma, St. Louis, Mo.) was applied at room temperature for 20 minutes.The sections were washed in water and then mounted. The red reactionproduct was used to avoid confusion in interpretation of those tumorsproducing melanin. A step omission control, in which the VEGF-D MAbswere omitted, was included as were isotype-matched controls with theLMM774 antibody.

FIGS. 7A-C show results with the same melanoma sample whereas FIGS. 7Dand 7E show results for a different tumor stained in the same batch.Islands of immunoreactive melanoma cells are indicated by a one (1)inside the arrows in FIGS. 7A and 7B, and immunoreactive blood vesselsare indicated a two (2) inside the arrows in 7C. Melanoma cells withvarying levels of VEGF-D are apparent in 7E. The magnification in FIGS.7A, 7D and 7E is approximately ×60, and in FIGS. 7B and 7C, it isapproximately ×300.

Positive reactions were seen with all four VEGF-D MAbs with essentiallythe same staining patterns. The results shown in FIGS. 7A-C and 7E werewith MAb 2F8. Assessment of the staining patterns by light microscopicexamination showed variable staining through the bulk of the melanomas.In the larger tumor, staining was more pronounced in small islands oftumor cells at the periphery of the invasive portions (FIGS. 7A and 7B)and in the intraepidermal nests of tumor cells, being less intense orundetectable in the central invasive portion of the tumor. Smallcapillary sized vessels in the papillary and reticular dermis adjacentto positive reacting tumor cells showed variable granular reaction tothe antibodies in the cytoplasm of endothelial cells (FIG. 7C). Thereaction for the smaller tumor was more even in distribution throughoutthe tumor mass (FIG. 7E). Blood vessels at a variable distance lateralto the tumor, and in the mid and deep reticular dermis and subcutaneoustissue away from the immunoreactive tumor cells did not show anyreaction with the VEGF-D MAbs. In contrast to the results with theVEGF-D MAbs, the LMM774 control in the same tumor was negative (FIG. 7D)as were the step omission controls.

It has been shown for some tumors that VEGF synthesis and secretion canbe switched on in hypoxic tumor cells and that the tumor can also induceexpression of VEGFR-2 in the endothelial cells of nearby blood vessels(Plate et al., Cancer Res., 1993 53 5822-5827). In this way a paracrinesystem is established for inducing tumor angiogenesis whereby VEGF,secreted in the tumor, diffuses through interstitium and binds toVEGFR-2 on target endothelial cells and thereby induces endothelial cellproliferation. The results for VEGF-D localization in melanomas indicatethat VEGF-D may be fulfilling a similar function in malignant melanomas.The VEGF-D MAbs detected VEGF-D in melanoma cells in both clinicalsamples tested. These tumor cells are most likely producing VEGF-D. Inaddition, VEGF-D was detected on the endothelial cells of blood vesselsin the vicinity of the producer tumor cells but not on more distantvessels. The VEGF-D is probably localized on these endothelial cells dueto interaction with VEGFR-2, a receptor for VEGF-D which is oftenexpressed on tumor blood vessels (Plate et al., Cancer Res., 1993 535822-5827). Further immunohistochemical analyses will be required toassess if VEGF-D is also localized on lymphatic vessels in the vicinityof the tumor. Such a scenario is feasible because lymphatic endothelialcells express VEGFR-3, a high affinity receptor for VEGF-D (Joukov etal., The EMBO Journal, 1996 15 290-298).

The results indicate that melanoma cells can express the VEGF-D gene.Analysis of mouse embryos at post-coital day 15.5 by in situhybridization showed expression of the VEGF-D gene immediately under thedeveloping skin, in a region rich in developing melanocytes andfibroblasts (Example 3 and FIGS. 5 and 6). Therefore it may be thattransformed melanocytes have re-acquired the capacity to express thegene for VEGF-D, as was the case during embryogenesis. If events otherthan oncogenic transformation can induce VEGF-D gene expression inmelanocytes, this protein could be involved in other types of skindisorders characterized by inflammation or proliferation of bloodvessels and/or lymphatic vessels. In a therapeutic setting, theapplication of VEGF-D in response to tissue damage may be useful forstimulating the growth of blood and lymphatic vessels adjacent toregenerating skin. Similarly, application of VEGF-D to stimulateangiogenesis and lymphangiogenesis is useful to enhance the success ofskin grafting procedures. These are used in the treatment of a varietyof conditions such as burns and other traumatic injuries, in avoiding orreducing surgical scarring, in cosmetic surgery, and the like.

Example 6 Testing Antibodies for the Capacity to Bind to VEGF-C

The enzyme immunoassay as described above was used to test the sixVEGF-D MAbs for the capacity to bind to VEGF-CΔNΔC. VEGF-CΔNΔC consistsof the VEGF homology domain of VEGF-C (residues 103 to 215) and is theregion of VEGF-C which is most similar to VEGF-DΔNΔC. VEGF-CΔNΔC, towhich a 6× histidine tag had been added at the C-terminus, was expressedin strain GS115 of the yeast P. pastoris using the expression vectorpIC9 (Invitrogen, San Diego, Calif.) according to manufacturer'sinstructions and purified using Ni-NTA Superflow resin (QIAGEN,Valencia, Calif.) Of the six antibodies tested by this immunoassay, only4E10 bound to VEGF-CΔNΔC.

Example 7 VEGF-D is Proteolytically Processed in a Similar Fashion toVEGF-C

In order to investigate the proteolytic processing of VEGF-D, 293-EBNAcells were stably transfected with pVDApexΔC, pVDApexFullNFlag,pVDApexΔNΔC (Example 1 and FIG. 1) and pVDApexFullCFlag. Theseexpression constructs encode VEGF-DΔC, VEGF-DFullNFlag, VEGF-DΔNΔC(Example 1 and FIG. 1) and VEGF-DFullCFlag respectively (FIG. 8). TheVEGF-D structural domains are shown at the top of FIG. 8. “SS” denotesthe signal sequence for protein secretion, N-terminal pro and C-terminalpro denote the propeptides and VHD denotes the VEGF homology domain.Beneath are shown the characterized and putative proteolytic cleavagesites in VEGF-D marked by arrows. The potential N-linked glycosylationsites are marked with asterisks. The region of VEGF-D used as theimmunogen to generate the A2 antiserum (described below) is shown by ablack bar. The bottom half of the figure shows the primary translationproducts for the VEGF-D derivatives expressed in 293-EBNA cells. Forsimplicity, the signal sequences for protein secretion have beenomitted. The FLAG octapeptide epitope is denoted by an a similar fashionas pVDApexFullNFlag (Example 1) except that the DNA for the endogenousVEGF-D signal sequence for protein secretion had been retained and the“Kozak” consensus sequence for translation initiation had been optimizedwhich necessitated insertion of the three amino acids “A-R-L”immediately after the initiation codon of VEGF-D. This construct alsoencoded the amino acids “A-R-Q” followed by the FLAG octapeptidesequence at the C-terminus of the protein. Since the 293-EBNA cell lineis capable of proteolytically processing VEGF-C (Joukov et al., EMBO J.,1997 16 3898-3911), this allows analysis of the VEGF-D derivativesderived from these transfected cells to be followed during cellularbiosynthesis and processing.

The VEGF-D derivatives were purified from the conditioned medium ofstably transfected 293-EBNA cells by affinity chromatography on M2(anti-FLAG) gel (Sigma-Aldrich) and eluted using the FLAG® peptideaccording to the manufacturer. The FLAG® peptide was removed using acentrifugal concentrator (Amicon, Beverly, Mass.). Aliquots of thefractions eluted from the M2 affinity columns were analyzed by SDS-PAGEand silver staining or immunoblotted with the M2 antibody(Sigma-Aldrich) to confirm the identity of the purified species.

Analysis of the 293-EBNA cells expressing the various VEGF-D derivativesby SDS-PAGE show that the VEGF-D polypeptide is proteolyticallyprocessed. Purification using medium from 293-EBNA cells expressingVEGF-DFullNFlag allowed specific analysis of only those VEGF-Dpolypeptides with the FLAG octapeptide at the N-terminus or ofderivatives bound covalently or non-covalently to the FLAG®-taggedpolypeptides (FIG. 8 and FIG. 11).

The polyclonal antiserum designated A2 was raised in rabbits against asynthetic peptide corresponding to the region of human VEGF-D fromresidues 190 to 205, KCLPTAPRHPYSIIRR (SEQ ID NO:3), which are in theVHD (SEQ ID NO:11).

For the SDS-PAGE and Western Blot analysis, samples containing thepurified VEGF-D derivatives were combined 1:1 with 2×SDS-PAGE samplebuffer, boiled and resolved by SDS-PAGE (Laemmli, Nature, 1970 227680-685). The proteins were then transferred to an Immobilon-P membrane(Millipore, Bedford, Mass.) and non-specific binding sites were blockedby incubation in 3% BSA, 100 mM Tris-HCl (pH 7.5), 150 mM NaCl and 0.02%Tween 20. Blots were then incubated with a 1:2000 dilution of A2antiserum for 2 hours at room temperature or alternatively with the M2(anti-FLAG) antibody as described by the manufacturer. After washing inbuffer (3% BSA, 100 mM Tris-HCl (pH 7.5), 150 mM NaCl and 0.02% Tween20) the blots were probed with anti-rabbit Ig horseradish peroxidase(HRP) conjugate or anti-mouse Ig HRP conjugate (Biorad, Hercules,Calif.) and developed using chemiluminescence (ECL, Amersham, UK).

Analysis of proteins secreted by cells expressing VEGF-DFullNFlag bySDS-PAGE under reducing conditions and silver staining revealed aspecies of approximately 53 kDa, the expected size of unprocessedVEGF-D, as well as two polypeptides of approximately 31 and 29 kDa (FIG.9A) The sizes of molecular weight markers (in kDa) are shown to the leftof each panel and the positions of the VEGF-D derivatives (withmolecular weights in kDa) are marked by arrows to the right. This resultis consistent with proteolytic cleavage events occurring near theC-terminus of the VHD. According to this model, the approximately 53 kDapolypeptide would represent unprocessed VEGF-D and the approximately 31kDa polypeptide would consist of the N-terminal propeptide and the VHD(i.e. lacking the C-terminal propeptide). The expected size of apolypeptide consisting of the N-terminal propeptide and the VHD isindeed approximately 31 kDa because the VHD, which is glycosylated, wasshown previously to be approximately 21 kDa (Achen et al., Proc. Natl.Acad. Sci. USA, 1998 95 548-553; FIG. 12b of PCT/US97/14696) and theexpected size of the FLAG-tagged N-terminal extension is approximately10 kDa. If processing of VEGF-D involves cleavage near the N-terminus ofthe VHD, in addition to the C-terminus of the VHD, cells expressingVEGF-DFullNFlag should also secrete a 10 kDa FLAG-tagged polypeptideconsisting only of the N-terminal extension. Although a 10 kDapolypeptide was not detected among the VEGF-D derivatives secreted bythese cells as assessed by silver staining (FIG. 9A), it was clearlydetected by Western blot analysis of the same material using the M2antibody (FIG. 9B). The approximately 29 kDa polypeptide detected bysilver staining was not detected in the same sample by Western blot withthe A2 polyclonal antiserum (FIG. 9C) and therefore would represent theC-terminal propeptide. This was confirmed by N-terminal amino acid ofthis polypeptide which identified the N-terminal sequence as “SIQIPEED”(SEQ ID NO:4), which is immediately adjacent to the predicted C-terminalcleavage site of the VHD based on comparison with VEGF-C. Therefore theC-terminal cleavage site in VEGF-D is located immediately after arginine205 (“R↓SIQIPEED”) (SEQ ID NO:5). It is most likely that thisapproximately 29 kDa polypeptide was present in the affinity-purifiedmaterial because of the interchain disulfide bonds between the—andC-terminal propeptides (see FIG. 11 for a scheme for VEGF-D processing).

To further examine the possibility of proteolytic cleavage of VEGF-Dnear the N-terminus of the VHD, proteins secreted by 293-EBNA cellsexpressing VEGF-DΔC were purified and analyzed as above. The constructfor VEGF-DΔC drives expression of a VEGF-D derivative in which theC-terminal extension has been deleted and replaced with FLAG (FIG. 8).Conditioned medium from these cells contained two FLAG-taggedpolypeptides of approximately 31 and 21 kDa as assessed by silverstaining (FIG. 9D). This result is consistent with an N-terminalcleavage event which occurs near the N-terminus of the VHD,approximately 10 kDa from the N-terminus of unprocessed VEGF-D. Thus theapproximately 31 kDa polypeptide would consist of the N-terminalextension and the VHD, whereas the approximately 21 kDa polypeptidewould consist of the VHD alone. Consistent with this model were thefindings that the both the approximately 31 and approximately 21 kDabands were detected by Western blot analysis with M2 antibody (FIG. 9E).Also as expected, both bands were detected by Western blot analysis withthe A2 antiserum (data not shown).

To determine the exact position of the N-terminal proteolytic cleavagesite in VEGF-D, the approximately 21 kDa polypeptide purified from thesupernatants of cells expressing VEGF-DΔC was subjected to N-terminalamino acid sequencing. N-terminal amino acid sequencing ofaffinity-purified protein was carried out using a Hewlett-PackardProtein Sequencer, model G1000A (Hewlett-Packard, Palo Alto, Calif.).The N-terminal sequence of this polypeptide was heterogeneous. Thepredominant sequence, representing approximately 80% of the materialbegan as “FAATFY” (SEQ ID NO:6) and a minor sequence, representing10-15% of the material began with “KVIDEE” (SEQ ID NO:7). Thus, asexpected, the N-terminus of the approximately 21 kDa polypeptide islocated at about the same position as the N-terminus of the VHD. Themajor N-terminal cleavage site in VEGF-D is located immediately afterarginine 88 (“R↓FAATFY”) (SEQ ID NO:8) and the minor cleavage site isimmediately after leucine 99 (L↓SKVIDEE) (SEQ ID NO:9) (FIG. 8).

Example 8 VEGF-DΔNΔC Exists Predominantly in the Form of a Non-CovalentDimer

In general, VEGF family members exist as disulfide-bonded homodimers.However, VEGF-CΔNΔC exists predominantly in the form of a non-covalentdimer (Joukov et al., EMBO J., 1997 16 3898-3911). The mature form ofVEGF-D, VEGF-DΔNproΔCpro, is also not a disulfide-linked dimer becausethis polypeptide migrates almost identically under reducing andnon-reducing conditions in SDS-PAGE. In order to test the nature of themature form of VEGF-D, affinity-purified VEGF-DΔNΔC was subjected tosize exclusion chromatography. Size exclusion chromatography was carriedout by loading the affinity-purified protein onto a TSKG2000SW (7.5×60mm Id) column (LKB Bromo, Sweden). The column was equilibrated with PBS.Proteins were eluted with a flow rate of 0.25 ml/min and 1 minutefractions collected. The protein elution was monitored at 215 nm. Threemajor peaks were eluted from the column with apparent molecular weights(shown above each peak in brackets) of 73 kDa (peak 1), 49 kDa (peak 2)and 25 kDa (peak 3) and the ratio of total protein in these peaks wasestimated spectrophotometrically to be approximately 1:2.1:0.9 (FIG.10A). The apparent molecular weights were determined using a calibrationcurve constructed from known proteins: bovine serum albumin dimer,bovine serum albumin, ovalbumin and trypsin inhibitor (Sigma Aldrich PtyLtd, Australia). The fractions corresponding to these peaks were pooled,concentrated to 100 μl using centrifugal concentrators and analyzed bySDS-PAGE under reducing conditions and silver stained (FIG. 10B). Tracks1, 2 and 3 correspond to protein from peaks 1, 2 and 3 respectively. Theposition of the VEGF-DΔNΔC subunit is shown in FIG. 10B to the left andthe positions of molecular weight markers (in kDa) are shown to theright.

The VEGF-DΔNΔC subunit (approximately 21 kDa) was most abundant in peak2, was easily detectable in peak 3 and was undetectable from peak 1(FIG. 10B). The predominant species in peak 1 was a 73 kDa protein whichis a contaminant that is often detected in samples of protein purifiedby M2 affinity chromatography and which cannot be detected by Westernblot analysis with either M2 antibody or A2 antiserum (data not shown).The 73 kDa protein was also observed in control M2 affinitypurifications using the supernatants from 293-EBNA cells which had beentransfected with Apex-3 plasmid lacking sequence encoding VEGF-D (datanot shown). The apparent molecular weights determined from the sizeexclusion chromatography indicated that the proteins in peaks 2 and 3were a VEGF-DΔNΔC dimer and the VEGF-DΔNΔC monomer respectively.Therefore, a non-covalent dimer, the subunits of which separate inSDS-PAGE under reducing or non-reducing conditions, was the predominantmolecular species in the affinity-purified preparations of VEGF-DΔNΔC.

The capacities of the dimeric and monomeric forms of VEGF-DΔNΔC to bindVEGFR-2 were assessed with fractions eluted from the column and assayingfor the capacity to bind VEGFR-2 using the Ba/F3 cell bioassay describedin International Patent application PCT/US95/16755. The VEGFR-2-bindingactivity in peak 3 was approximately 2% of that in peak 2, indicatingthat the VEGF-DΔNΔC non-covalent homodimer is much more bioactive thanthe monomer. The VEGFR-2 binding activity in peak 1 was approximately 1%of that in peak 2, presumably reflecting a small amount of theVEGF-DΔNΔC non-covalent homodimer in this peak. Clearly the dimeric formof VEGF-DΔNΔC binds far better to VEGFR-2 than does the monomeric form.

The data presented in Example 6 demonstrates that VEGF-D isproteolytically processed and that the sites of proteolytic cleavage aresimilar in location, but not identical, to those in VEGF-C. Theproteolytic processing is likely to be of considerable biologicalimportance because different VEGF-D derivatives have differentcapacities for activating VEGF receptors. Whereas fully processed VEGF-Dbinds and activates both VEGFR-2 and VEGFR-3 (Achen et al., Proc. Natl.Acad. Sci. USA, 1998 95 548-553) the unprocessed form of VEGF-Dactivates VEGFR-3 but not VEGFR-2 (FIGS. 14 and 15 of PCT/US97/14696).Therefore step-wise proteolytic processing may be a way to regulate thereceptor-binding specificity of VEGF-D in vivo.

Size exclusion chromatography also demonstrated that affinity-purifiedVEGF-DΔNΔC is predominantly a non-covalent dimer but that a smallproportion is monomeric. Only the dimeric form could strongly activate achimeric receptor containing the extracellular domain of VEGFR-2. Thisfinding was expected, given that activation of cell surface receptortyrosine kinases involves receptor dimerization. Presumably the dimericligand provides two receptor binding sites per molecule whereas themonomeric form provides only one: Thus the dimeric ligand can inducereceptor dimerization but the monomeric ligand cannot.

A scheme for the processing of VEGF-D as carried out by 293-EBNA cellswhich would give rise to monomers and dimers is shown in FIG. 11. Twodistinct forms of unprocessed VEGF-D are secreted from the cell: amonomer (left side) and an anti-parallel disulfide-linked dimer withdisulfide bridges between the—and C-terminal propeptides (right side).Arrows lead from the intracellular forms to the products of stepwiseproteolytic processing at the—and C-termini of the VHD which ultimatelygive rise to mature forms of VEGF-D that consist of a non-covalent dimerand a monomer of the VHD. Analyses of VEGF-D derivatives from the celllines described here suggest that cleavage of the C-terminal propeptidefrom the VHD is more efficient than cleavage of the N-terminalpropeptide. For simplicity, not all possible derivatives arising fromproteolytic processing are shown. In FIG. 11, N-pro denotes N-terminalpropeptide; C-pro, the C-terminal propeptide; VHD, the VEGF homologydomain; grey boxes, non-covalent interactions between domains; —S—,intersubunit disulfide bridges; N—, the N-termini of polypeptides; andthe arrowheads represent the approximate locations of proteolyticcleavage sites.

Example 9 VEGF-D and Vascular Permeability

Affinity-purified human VEGF-DΔNΔC was tested for the capacity to inducevascular permeability using the Miles assay. The Miles assay (Miles, A.A. and Miles, E. M., J. Physiol., 1952 118 228-257) was performed usinganesthetized guinea pigs. For quantitation of extravasation induced bypermeability factors, the area of sample injection was excised and theEvans Blue dye extracted by a three day incubation in formamide at42.degree. C. The amount of dye extracted was quantitatedspectrophotometrically by reading the absorbance of the samples at 620nm. VEGF-DΔNΔC was used because the VHD of human VEGF-C (VEGF-CΔNΔC) isknown to induce vascular permeability (Joukov et al., EMBO J., 1997 163898-3911). Purified mouse VEGF₁₆₄ was included as a positive control.As expected, mouse VEGF₁₆₄ strongly induced vascular permeability. Thelowest concentration of mouse VEGF₁₆₄ which induced detectable vascularpermeability was 60 ng/ml. Likewise, human VEGF-CΔNΔC also inducedvascular permeability, however the lowest concentration with detectableactivity was 250 ng/ml. In contrast, VEGF-DΔNΔC showed no activity, evenat protein concentrations as high as 1 μg/ml. These results indicatethat human VEGF-DΔNΔC is not an inducer of vascular permeability inguinea pigs.

VEGF-D and VEGF-C are considered members of a sub-family of the VEGFfamily (Achen et al., Proc. Natl. Acad. Sci. USA, 1998 95 548-553)because of similarities in primary structure and receptor-bindingspecificity. The mechanisms of processing of these two molecules aresimilar, but not identical. However, these two growth factors exhibitdifferences in bioactivities as illustrated by the finding thatVEGF-DΔNΔC does not induce vascular permeability. In contrast,VEGF-CΔNΔC does induce vascular permeability although not as potently asVEGF (Joukov et al., EMBO J., 1997 16 3898-3911).

The foregoing description and examples have been set forth merely toillustrate the invention and are not intended to be limiting. Sincemodifications of the disclosed embodiments incorporating the spirit andsubstance of the invention may occur to persons skilled in the art, theinvention should be construed broadly to include all variations fallingwithin the scope of the appended claims and equivalents thereof.

1. A mammalian cell line transformed or transfected with a promoteroperably linked to a VEGF-D nucleic acid, wherein the VEGF-D nucleicacid comprises a nucleotide sequence encoding a continuous portion ofSEQ ID NO: 11 having a biological activity of VEGF-D selected from thegroup consisting of ability to stimulate one or more of endothelial cellproliferation, differentiation, migration, survival or vascularpermeability, wherein the VEGF-D nucleic acid lacks the codons encodingamino acids 203-354 of SEQ ID NO: 11; and wherein said promoter iscapable of promoting expression of the nucleic acid in a mammalian cell.2. A mammalian cell line transformed or transfected with a promoteroperably linked to a VEGF-D nucleic acid, wherein the VEGF-D nucleicacid comprises a nucleotide sequence encoding a continuous portion ofSEQ ID NO: 11 having a biological activity of VEGF-D selected from thegroup consisting of ability to stimulate one or more of endothelial cellproliferation, differentiation, migration, survival or vascularpermeability, wherein the VEGF-D nucleic acid lacks the codons encodingamino acids 203-354 of SEQ ID NO: 11, and wherein said cell line is the293-EBNA human embryonal kidney cell line.
 3. A mammalian call linetransformed or transfected with a promoter operably linked to a VEGF-Dnucleic acid, wherein the VEGF-D nucleic acid comprises a nucleotidesequence encoding a continuous portion of SEQ ID NO: 11, wherein theVEGF-D nucleic acid encodes amino acids 2-202 of SEQ ID NO: 11 andwherein the VEGF-D nucleic acid lacks the codons encoding amino acids203-354 of SEQ ID NO:
 11. 4. An expression vector comprising a nucleicacid comprising a nucleotide sequence encoding a continuous portion ofSEQ ID NO:11 having a biological activity of VEGF-D selected from thegroup consisting of ability to stimulate one or more of endothelial cellproliferation, differentiation, migration, survival or vascularpermeability, wherein the nucleic acid lacks the codons encodingpositions 203-354 of SEQ ID NO: 11, and, a promoter operably linked tothe nucleic acid, wherein said promoter is capable of promotingexpression of the nucleic acid in a mammalian cell.
 5. An isolatednucleic acid comprising a nucleotide sequence encoding a continuousportion of SEQ ID NO:11 having a biological activity of VEGF-D selectedfrom the group consisting of ability to stimulate one or more ofendothelial cell proliferation, differentiation, migration, survival orvascular permeability, wherein the nucleic acid lacks the codonsencoding amino acids 203-354 of SEQ ID NO:
 11. 6. The isolated nucleicacid according to claim 5, further comprising sequence that encodes anaffinity tag attached in-frame to the nucleotide sequence.
 7. Anexpression vector comprising the nucleic acid according to claim
 6. 8.An isolated host cell transformed or transfected with the isolatednucleic acid of claim 5 or the vector according claim 4.